The present invention relates to instruments for sensing the instantaneous pressure in a combustion chamber such as in the combustion chamber of a reciprocating internal combustion engine. Combustion chamber pressure transducers have found particular application in reciprocating internal combustion engines for detecting combustion anomalies such as detonation or "knocking", misfiring and pre-ignition. Pressure transducers of this type are typically mounted through a port in the combustion chamber such as a threaded hole in the cylinder head and are employed for knock sensing to provide an electrical signal to an engine control computer for controlling retarding of the ignition spark timing to prevent knocking. Knock sensors have become a critical element in the management of the spark ignition timing in reciprocating internal combustion engines employed for passenger and light truck automotive engines for controlling the exhaust emissions.
Heretofore, knock sensors or transducers for internal combustion engine usage have employed a metal diaphragm exposed to the combustion chamber gasses which moved an intermediate member to provide a force against a sensing element to generate an electrical signal indicative of the combustion pressure forces on the pressure responsive diaphragm. The problem of providing the motion transmitter or linkage between the pressure responsive diaphragm exposed to the combustion gasses and the sensing element has resulted in a transducer which did not have the desired response time to properly track the pressure increases due to detonation or knocking; and, thus the transducer was not capable of providing an adequate electrical signal for enabling the engine controller to retard timing in a timely fashion to adequately attenuate incipient knocking. Thus it has been desired to provide a combustion chamber pressure transducer capable of responding instantaneously to the unusually high combustion chamber pressures resulting from detonation and knocking in order to enable the engine controller to respond with changes in ignition timing to eliminate the detonation or knocking. In addition, the extremely high temperatures of the combustion event apply steep temperature gradients and high heat loads to the face and internals of the device as it is positioned in the wall of the combustion chamber. The high temperatures affect the response, performance and location of the sensing element resulting in higher cost for the transducer capable of functioning in such an environment.